Tokkai Hei 6-44500 and Tokkai Hei 6-27238 published by the Japanese Patent Office in 1994 disclose a device for preventing vehicle collision by calculating a minimum safe distance according to the vehicle speed, using a laser radar that measures the distance to the vehicle in front and a speed sensor for detecting the speed of the vehicle. When the distance to the vehicle in front falls below this minimum distance, the device warns the driver of the vehicle by means of a sound or vibration.
When the driver recognizes the danger, he has to slow down to avoid a collision.
However, this device merely emits an alarm, and it does not directly relate to the braking operation the driver has to take in response to the alarm.